Rh

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Of or relating to the Rh factor: an Rh antigen; the Rh blood group; Rh incompatibility.
2. The symbol for the element rhodium.

Century Dictionary and Cyclopedia

1. An initial sequence, originally an aspirated r, occurring in English, etc., in words of Greek origin. In early modern and Middle English, as well as in Spanish, Italian, Old French, etc., it is also or only written r. When medial, as it becomes in composition, the r is doubled, and is commonly written rrh, after the Greek form ρ\ρ\, which, however, is now commonly written ρρ. In modern formations medial rrh is often reduced to rh. (For examples of rh, see the words following, and catarrh, diarrhea, hemorrhage, myrrh, pyrrhic, etc.) The combination rh properly occurs only in Greek words; other instances are due to error or confusion, or are exceptional, as in rhyme for rine, rhine for rine, rhone for rone, etc.
2. The chemical symbol of rhodium.
3. n. An abbreviation of Royal Horse Artillery.
4. n. An abbreviation of Royal Horse Guards.

Wiktionary

1. n. chemistry Symbol for rhodium.
2. medicine The Rhesus factor.

WordNet 3.0

1. n. any of several hormones produced in the hypothalamus and carried by a vein to the anterior pituitary gland where they stimulate the release of anterior pituitary hormones; each of these hormones causes the anterior pituitary to secrete a specific hormone
2. n. a white hard metallic element that is one of the platinum group and is found in platinum ores; used in alloys with platinum
3. n. a blood group antigen possessed by Rh-positive people; if an Rh-negative person receives a blood transfusion from an Rh-positive person it can result in hemolysis and anemia